Micom P634 - Negative-Sequence Current Stage

It is also possible to select whether the starting decision shall be based on the
fundamental or on the r.m.s. value.
The IDMT protection function will be triggered when the 1.05-fold of the set
reference current value is exceeded in one phase. The P634 will then determine
the maximum current flowing in the three phases and this value is used for
further processing.
Depending on the characteristic selected and the current magnitude, the P634
will determine the tripping time. Furthermore, a minimum tripping time can be
set; the tripping time will not fall below this minimum independently of the
magnitude of the current.
The IDMT protection function can optionally be blocked by the inrush stabilization
function of differential protection.
3.24.4 Negative-Sequence Current Stage
The P634 calculates the negative-sequence current from the three phase current
values according to this equation. This is based on the setting at MAIN: Phase
sequence.
Phase sequence A-B-C:
I
neg
=
1
3
⋅
| (
I
A
+ a
2
I
B
+ aI
C
) |
Phase sequence A-C-B:
I
neg
=
1
3
⋅
| (
I
A
+ aI
B
+ a
2
I
C
) |
a = e
j120°
a
2
= e
j240°
The negative-sequence current is monitored by the P634 to detect when it
exceeds the set thresholds. Alternatively, two different thresholds can be active.
The “dynamic” thresholds are active for the set hold time for the “dynamic
parameters” (see Section 3.12.8, (p. 3-88)) and the “normal” thresholds are
active when no hold time is running. The IDMT protection will trigger when the
1.05-fold of the set reference current value is exceeded. Dependent on the
characteristic selected and the negative-sequence current magnitude the P634
will determine the tripping time. Furthermore, a minimum tripping time can be
set; the tripping time will not fall below this minimum independent of the
magnitude of the current.
The negative-sequence current stage of the IDMT protection function can
optionally be blocked by the inrush stabilization function of differential
protection.
P634
3 Operation
3-168 P634/EN M/R-42-A // P634‑311‑653